1. Field of the Invention
The present invention relates to a temperature sensor circuit configured with a semiconductor integrated circuit.
2. Description of the Related Art
A conventional temperature sensor circuit configured with a semiconductor integrated circuit is shown in FIG. 6. In general, in a temperature sensor circuit, a collector and a base of a bipolar transistor 12 are set at the same electric potential, and an emitter thereof is connected to a constant current source 11. That is to say, the bipolar transistor 12 is diode-connected, thereby outputting a base to emitter voltage (hereinafter referred to as “a VBE” for short) of the bipolar transistor 12 to an output terminal 10. In this case, it is generally known that the VBE is independent of a current value of the constant current source 11, and hence has a certain constant voltage value. Thus, when there is made a request to output an arbitrary voltage to the output terminal 10, it is difficult to respond to this request.
Next, a temperature sensor circuit configured with a base-to-emitter voltage multiplication circuit (hereinafter referred to as “a VBE multiplication circuit” for short) 18 is shown in FIG. 7. With respect to a configuration of the VBE multiplication circuit 18, an emitter of a bipolar transistor 12 is connected to a constant current source 11 and one terminal of a first resistor 13, and the first resistor 13 and a second resistor 14 are connected in series with each other through their adjacent terminals. In addition, the grounding terminal of the second resistor 14 and a collector of the bipolar transistor 12 are set at the same electric potential, i.e., at the grounding electric potential, and a base of the bipolar transistor 12 is connected to a node between the first and second resistors 13 and 14. In this case, when an output voltage at an output terminal 10 is assumed to be expressed by VOUT, a resistance of the first resistor 13 is assumed to be expressed by R1, and a resistance of the second resistor 14 is assumed to be expressed by R2, and currents caused to flow through the first and second resistors 13 and 14 are assumed to be equal to each other, the output voltage VOUT is expressed by Equation (1):VOUT=VBE×(R1+R2)/R2  (1)From the foregoing, it is known that when the temperature sensor circuit is configured as shown in FIG. 7, the output voltage VOUT can be set to an arbitrary voltage depending on ratios of the resistance value of the first resistor 13 to the resistance value of the second resistor 14 (refer to a literature of “Analysis and Design of Analog Integrated Circuits”, by P. R. Gray and R. G. Meyer, (pp. 268 to 270 and FIG. 4.27(a)).
However, a base current IB of the bipolar transistor 12 is also caused to flow through the second resistor 14. At this time, when a current caused to flow through the first resistor 13 is assumed to be expressed by I1, and a current caused to flow through the second resistor 14 is assumed to be expressed by I2, Equation (2) is obtained:I2=I1+IB  (2)Thus, an error occurs in the currents caused to flow through the first and second resistors 13 and 14 due to the base current IB of the bipolar transistor 12. Consequently, it is difficult to set the output voltage VOUT as aimed using Equation (2). Moreover, it is difficult to set the output voltage VOUT as aimed owing to the dispersion in the characteristics of the bipolar transistor 12 and the characteristics of the two resistors 13 and 14.